In hybrid vehicles two drive units are combined with one another, which provide different types of power for driving the vehicle. The features of an internal combustion engine and an electric motor complement each other particularly well, therefore present hybrid vehicles are predominantly equipped with such a combination. In serial hybrid concepts the drive generally occurs via the electric motor, while the internal combustion engine provides electricity via a generator for charging the electric storage unit and/or for directly feeding the electric motor. However, today parallel hybrid concepts are preferred, in which the vehicle drive is provided both by the internal combustion engine as well as the electric motor.
In parallel hybrid concepts it is possible, in the different operational conditions of a vehicle to use the drive source with the better effectiveness under the given range of rpm-load ration. The electric motor can be connected to the drive train and/or the camshaft of the internal combustion engine in different manners. Preferred possibilities are the connection via a clutch or directly to the camshaft of the motor. Another possibility for a connection is a coupling via a belt drive or a transmission.
The operation of a hybrid vehicle by the electric motor can occur, for example, in operational conditions under a low load only, in which the internal combustion engine has only a low effectiveness. Operational conditions under higher loads can be used to recharge the energy storage unit by the internal combustion engine with its relatively wide range of effectiveness using additional generator operation of the electric motor. During motor operation the electric motor is supplied by the energy storage units. Additionally, a parallel momentum can also be supplied by the internal combustion engine and the electric motor, in order to increase the maximum torque of the entire drive, for example.
Ideally, at least a portion of the energy necessary for driving the vehicle and supplying the electric vehicle circuits is yielded from prior recuperation processes. It is common knowledge that here deceleration phases of the vehicle are used for energy recovery, by providing the necessary braking force of the vehicle by a generator operation of the electric motor to an extent as much as possible, in order to recharge the energy storage unit. Due to the fact that otherwise the energy loss in the brake system of the vehicle is converted into heat, there is a great potential optimizing the consumption of the vehicle drive.
From DE 199 47 922 A1 a method for a recuperating operation of a hybrid vehicle is already known, in which an electric motor in drive operation and/or in the generator operation. In the generator operation kinetic vehicle energy is converted into electricity by the electric motor and stored in an energy storage unit. Here, in a cycle it is first examined if the vehicle is to be driven or braked; after a drive request has been established it is tested if the supply of energy by the energy storage unit is permissible within the limits given. When the supply is allowed the energy is supplied therefrom and provided for the drive of the vehicle. When the supply is not allowed the energy is only provided by the primary drive. When no drive is requested, it is examined if braking is requested. In the case of braking being requested it is examined, if energy may be fed into the energy storage unit within the limits given. When the feeding of energy is allowed here, then kinetic energy of the vehicle is stored in the energy storage unit. When energy may not be fed (to the storage unit), it is fed to an energy disposal unit and subsequently the cycle is repeated. If in the first cycle it is determined that no drive is requested, for example by the accelerator not being operated, it is reviewed if braking is requested, for example by the operation of the brake pedal. If the brake pedal has been operated and energy is allowed to be fed to the energy storage unit, energy is fed to the energy storage unit and stored there.
It is further known from prior art to provide the entire braking momentum to the vehicle when the driver requests braking, beginning with a position of the braking pedal equaling zero, distributed into a portion provided by conventional vehicle brakes, and a portion created by the generator operation of the electric motor. In such a recuperation strategy a portion of the deceleration energy of the vehicle is always converted by the vehicle brakes into heat without being utilized. Further, from prior art an improved method is known, in which a first portion with requirements of only little braking momentum is initially covered entirely by the generator operation of the electric motor. This may occur, for example, in that the leeway of the brake pedal is utilized to provide even a low-level generator momentum of the electric motor. The vehicle brakes are activated only when a level has been exceeded, so that a higher potential of recuperation is utilized compared to the above-described method.